Liquid crystal display device

ABSTRACT

A liquid crystal display device includes: a pair of substrates at least one of which is transparent; a liquid crystal layer disposed between the pair of substrates; an electrode group formed on at least one substrate of the pair of substrates, for applying an electric field to the liquid crystal layer; a plurality of active elements connected to the electrode group; and a liquid crystal alignment film disposed on at least one substrate of the pair of substrates, in which the liquid crystal alignment film, which is formed by a photo-alignment process, contains polyimide formed using tetracarboxylic acid dianhydride and/or diamine each having a specific chemical structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 12/908,313, filed Oct. 20, 2010, the contents of which areincorporated herein by reference.

The present application claims priority from Japanese application JP2009-244721 filed on Oct. 23, 2009, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device. Morespecifically, the present invention relates to a liquid crystal displaydevice having a liquid alignment film formed by a photo-alignmentmethod.

2. Description of the Related Art

In general, a liquid crystal display device performs a display using achange in optical characteristics of a liquid crystal layer caused byapplying an electric field to liquid crystal molecules in a liquidcrystal layer sandwiched between a pair of substrates to change thealignment of the liquid crystal molecules.

In a pair of substrates, a liquid crystal alignment film typically madeof polyimide, polyamic acid, or the like is provided on an interfacebetween a liquid crystal layer and a substrate and plays a role ofaligning liquid crystal molecules in the liquid crystal layer in apredetermined direction.

As an industrial method of providing an organic coating film formed ofpolyimide or the like with a function of aligning liquid crystalmolecules (hereinafter, referred to as “alignment capability”), arubbing alignment process is widely known.

The rubbing alignment process is a method of rubbing the surface of anorganic coating film formed on the surface of a substrate with a clothmade of nylon, polyester, or the like in a predetermined direction. Thisprovides the surface of the organic coating film with alignmentcapability in the rubbed direction.

The rubbing alignment treatment is an industrially effective methodbecause the treatment can provide the surface of an organic coating filmwith uniform alignment capability relatively easily and in addition, isexcellent in productivity. However, along with the recent enlargement ofliquid crystal display devices, problems of the rubbing alignmenttreatment have come to be pointed out.

As described above, the rubbing alignment treatment includes the step ofallowing an organic coating film and a cloth to rub against each otherphysically. Therefore, unwanted shavings (scrapings) may be generated onthe surface of the liquid crystal alignment film thus formed. Theshavings cause display defects in a liquid crystal display device. Theamount of shavings increases along with the enlargement of a liquidcrystal display device, and hence there is apprehension that a defectoccurrence ratio may increase. Consequently, there is a demand for theestablishment of a treatment method that can replace the rubbingalignment treatment.

As an alignment treatment method replacing the rubbing alignmenttreatment, a photo-alignment process is known. The photo-alignmentprocess is a method of providing a surface of an organic coating filmwith alignment capability by irradiating the surface of the organiccoating film formed on the surface of a substrate with substantiallylinearly polarized UV rays (see, for example, U.S. Pat. No. 3,937,432).

SUMMARY OF THE INVENTION

The photo-alignment process is a clean alignment treatment method thatdoes not allow shavings to be generated through a step.

However, the irradiation of polarized UV rays in the step of thephoto-alignment process also influences a substrate to be coated withthe organic coating film. For example, there arises such a new problemthat a member forming the substrate may be damaged by irradiating thesubstrate with UV rays. In order to avoid such problem, it is necessaryto conduct the photo-alignment process at a low exposure amount. Inorder to realize the photo-alignment process at the low exposure amount,it is necessary to enhance sensitivity with respect to light exposure ofthe organic coating film.

An object of the present invention is to provide a liquid crystaldisplay device having a liquid crystal alignment film with highsensitivity with respect to light exposure. Further, the above-mentionedobject, another object, and new features become apparent from thedescription of the present specification and the attached drawings.

A liquid crystal display device according to the present inventionincludes: a pair of substrates at least one of which is transparent; aliquid crystal layer disposed between the pair of substrates; anelectrode group formed on at least one substrate of the pair ofsubstrates, for applying an electric field to the liquid crystal layer;a plurality of active elements connected to the electrode group; and aliquid crystal alignment film disposed on at least one substrate of thepair of substrates, in which the liquid crystal alignment film, which isformed by a photo-alignment process, contains polyimide formed using atleast one kind of tetracarboxylic acid dianhydride selected from acompound group A represented by the following Chemical Formulae (1) to(7).

In the formulae (1) to (7), R₁s each independently represent hydrogen,an alkyl group having a carbon number of 3 or less, or a dialkylaminogroup, and at least one R₁ is a dialkylamino group.

Further, S represents —(CH₂)_(n)—, and n represents an integer of 1 to10.)

Thus, there can be provided a liquid crystal display device having aliquid crystal alignment film with high sensitivity with respect to thelight exposure in photo-alignment.

Further, a liquid crystal alignment device according to the presentinvention includes: a pair of substrates at least one of which istransparent; a liquid crystal layer disposed between the pair ofsubstrates; an electrode group formed on at least one substrate of thepair of substrates, for applying an electric field to the liquid crystallayer; a plurality of active elements connected to the electrode group;and a liquid crystal alignment film disposed on at least one substrateof the pair of substrates, in which the liquid crystal alignment film,which is formed by a photo-alignment process, contains polyimide formedusing at least one kind of diamine selected from a compound group Brepresented by the following Chemical Formulae (8) to (10).

Among R₂s contained in each of the formulae (8) to (10), at least twoR₂s each independently represent a methyl group, an alkoxy group havinga carbon number of 3 or less, a dialkylamino group, or an alkylaminogroup and the other R₂s each independently represent hydrogen or analkyl group having a carbon number of 3 or less.

Thus, there can be provided a liquid crystal display device having aliquid crystal alignment film with high sensitivity with respect to thelight exposure in photo-alignment.

Thus, there can be provided a liquid crystal display device having aliquid crystal alignment film with high sensitivity with respect to thelight exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a pixel portion, illustrating apixel configuration of a liquid crystal display device according to anembodiment of the present invention.

FIG. 2A is a plan view of a pixel portion, illustrating a pixelconfiguration of a liquid crystal display device according to anembodiment of the present invention.

FIG. 2B is a cross-sectional view of a pixel portion, illustrating apixel configuration of a liquid crystal display device according to anembodiment of the present invention, which is a view illustrating across-section taken along line 2B-2B of FIG. 2A.

FIG. 2C is a cross-sectional view of a pixel portion, illustrating apixel configuration of a liquid crystal display device according to anembodiment of the present invention, which is a view illustrating across-section taken along line 2C-2C of FIG. 2A.

DETAILED DESCRIPTION OF THE INVENTION

A liquid crystal display device according to the present invention, forexample, includes: a pair of substrates at least one of which istransparent; a liquid crystal layer disposed between the pair ofsubstrates; an electrode group formed on at least one substrate of thepair of substrates, for applying an electric field to the liquid crystallayer; a plurality of active elements connected to the electrode group;and a liquid crystal alignment film disposed on at least one substrateof the pair of substrates, in which the liquid crystal alignment film,which is formed by a photo-alignment process, contains polyimide formedusing at least one kind of tetracarboxylic acid dianhydride selectedfrom a compound group A represented by the following Chemical Formulae(1) to (7).

In the formulae (1) to (7), R₁s each independently represent hydrogen,an alkyl group having a carbon number of 3 or less, or a dialkylaminogroup, and at least one R₁ is a dialkylamino group.

Further, S represents —(CH₂)_(n)—, and n represents an integer of 1 to10.

With the above-mentioned formulae, a liquid crystal display devicehaving a liquid crystal alignment film with satisfactory exposuresensitivity can be obtained.

The exposure sensitivity in the present invention is evaluated based onthe exposure amount (irradiation energy) to be required until thephoto-alignment process is completed. Further, the exposure amount isobtained by a product of an illumination by an irradiation time.

In the case where the exposure sensitivity of an organic coating filmformed on a substrate is satisfactory, the organic coating film becomesa liquid crystal alignment film through a photo-alignment process at alow exposure amount.

The liquid crystal alignment film in the present invention ischaracterized by being provided with alignment capability through aphoto-alignment process.

The photo-alignment process is a method of irradiating the surface of aformed organic coating film with substantially linearly polarized UVrays. Thus, the organic coating film is provided with alignmentcapability to be a liquid crystal alignment film.

With the photo-alignment process, the organic coating film is irradiatedwith UV rays to cause a structural change in a part of the molecularstructure of a compound constituting the organic coating film, andhence, the organic coating film is provided with alignment capability.

For example, in molecular structures of polyimide and a precursorthereof, alignment capability is provided through a process in which apart of the molecular structures of polyimide and the precursor thereofis cleaved due to the irradiation of UV rays.

More specifically, the exposure amount required for realizingphoto-alignment is the amount of energy that can cause theabove-mentioned structural change. Respective organic coating films thatcan form a liquid crystal alignment film by a photo-alignment processare different in exposure amount required for realizing aphoto-alignment process depending upon the compositions of compoundsconstituting the organic coating films.

In the case of conducting a photo-alignment process using the same lightsource, an organic coating film with exposure sensitivity improved canshorten an irradiation time of the photo-alignment process. In addition,when a lamp with a high illumination is used, an irradiation time isfurther shortened.

When UV rays are irradiated in the photo-alignment process, thegeneration of ozone also increases along with the increase in exposureamount. The generated ozone damages another member provided on asubstrate, and may cause a problem such as degradation in performance ofa liquid crystal display device. Conducting a photo-alignment processwith a low exposure amount means that the above-mentioned problems canbe avoided.

The liquid crystal alignment film provided in the liquid crystal displaydevice obtained in the present invention has high sensitivity withrespect to the light exposure, while having characteristics such as ahigh light transmittance (less absorption of visible light), heatresistance, high coating film strength, and a function of aligningliquid crystal molecules (hereinafter, referred to as “alignmentcapability”).

Compounds represented by Chemical Formulae (1) to (7) react with diamineto form polyamic acid and/or a polyamic acid ester that are precursorsof polyimide. Further, the polyamic acid and/or polyamic acid ester formpolyimide by an imidization reaction.

A liquid crystal alignment film formed of polyimide and a precursorthereof has characteristics such as a high light transmittance (lessabsorption of visible light), heat resistance, high coating filmstrength, and a function of aligning liquid crystal molecules(hereinafter, referred to as “alignment capability”), and hence, is usedwidely in a liquid crystal display device.

Examples of diamine that reacts with the compounds represented byChemical Formulae (1) to (7) include p-phenylenediamine,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulfide, and1,5-diaminonaphthalene. These diamines can be used alone or incombination of two or more kinds, for the reaction with the compoundsrepresented by Chemical Formulae (1) to (7).

Further, the polyamic acid ester can be obtained by allowing achlorinated reagent such as thionyl chloride to react withdiesterdicarboxylic acid obtained by allowing alcohol to react with atetracarboxylic acid dianhydride represented by Chemical Formulae (1) to(7) to obtain diesterdicarboxylic acid chloride, and then allowingdiamine to react with and to be polycondensed with thediesterdicarboxylic acid chloride.

Furthermore, in the case where diamine and a plurality of kinds ofmaterials of a tetracarboxylic acid dianhydride are mixed, acopolymerized polymer in which a plurality of chemical species ispolymerized with one polymer chain can be obtained.

Polyimide constituting the liquid crystal alignment film is formed byheating polyamic acid and/or a polyamic acid ester that are precursorsthereof, and allowing an imidization reaction (intramolecularcondensation reaction) to proceed.

Further, it is preferred that polyimide with a high molecular weightconstitute a liquid crystal alignment film, in terms of providing theliquid crystal alignment film with alignment capability. A polyamic acidester is unlikely to cause a decomposition reaction during heating,compared with polyamic acid. More specifically, the polyamic acid esteris unlikely to undergo any decrease in molecular weight in a heatingstep described later. Therefore, it is effective that a polyamic acidester is introduced into a liquid crystal alignment film, in terms ofpreventing the decrease in molecular weight of polyimide.

Next, the step of forming a liquid crystal alignment film containingpolyimide is described.

Polyimide is insoluble in a number of oil solvents. Therefore, in thecase of forming a liquid crystal alignment film containing polyimide asa main component, polyamic acid and/or a polyamic acid ester that areprecursors of polyimide are dissolved in a solvent to prepare a liquidcrystal alignment agent varnish, the varnish is applied to at least oneof a pair of substrates, on which the liquid crystal alignment film isto be formed, followed by heating and imidization, alignment treatmentis conducted, and thus, a liquid crystal alignment film of polyimide isformed.

In the above-mentioned heating step, the solvent contained in the liquidcrystal alignment agent varnish is volatilized, and an organic coatingfilm of polyamic acid and/or a polyamic acid ester is formed. At thesame timing as that in the formation of the organic coating film, theimidization reaction of polyamic acid and/or a polyamic acid esterproceeds.

It is not always necessary to progress the imidization reaction by 100%,and the imidization reaction is advanced preferably by 40% to 100% ofthe total, more preferably by 50% to 95%, and still more preferably by60% to 90%.

The polyimide and the precursor thereof formed using the compoundsrepresented by Chemical Formulae (1) to (7) are preferred for providingalignment capability in the photo-alignment process.

When the polyimide and the precursor thereof formed using the compoundsrepresented by Chemical Formulae (1) to (7) are irradiated with UV rays,an intermediate is formed in the molecular structure of the polyimideand the precursor thereof.

The intermediate thus formed is considered to act on photo-alignmenteffectively. In order to perform a photo-alignment process effectively,it is important how easily the intermediate is formed.

The formation of the above-mentioned intermediate in the molecularstructures of the polyimide and the precursor thereof is ascribed to thecleavage of a part of the molecular structures of the polyimide and theprecursor thereof caused by the irradiated UV rays.

Thus, in order to conduct a photo-alignment process effectively, it isnecessary that a part of the molecular structures of polyimide and aprecursor thereof is cleaved at high sensitivity by the irradiated UVrays.

The compounds represented by Chemical Formulae (1) to (7) arecharacterized by having a dialkylamino group that is an electrondonating group in the molecular structure thereof.

The polyimide and the precursor thereof formed using the compoundsrepresented by Chemical Formulae (1) to (7) have a dialkylamino groupderived from the compounds represented by Chemical Formulae (1) to (7)in the molecular structure.

The inventors of the present invention have found that, in the casewhere polyimide and a precursor thereof having a dialkylamino group inmolecular structures are irradiated with UV rays to be irradiated in aphoto-alignment process, an intermediate is formed in molecularstructures of the polyimide and the precursor thereof at a low exposureamount.

The liquid crystal alignment film provided in the liquid crystal displaydevice of the present invention realizes the enhanced sensitivity withrespect to UV rays irradiated in the photo-alignment process due to thefact that a dialkylamino group that is an electron donating group iscontained in molecular structures of polyimide and a precursor thereofconstituting the liquid crystal alignment film.

Thus, the UV irradiation amount in the photo-alignment process can bereduced.

The case where all of R₁ in the molecular structures in the compoundsrepresented by Chemical Formulae (1) to (7) are methyl groups that areelectron donating groups is compared with the case where one of R₁ is adialkylamino group. In the case where one of R₁ is a dialkylamino group,a liquid crystal alignment film with further satisfactory exposuresensitivity can be obtained. However, the addition of methyl groups tothe molecular structures of the compounds represented by ChemicalFormulae (1) to (7) is effective for enhancing exposure sensitivity.

Thus, it is more preferred that R₁s contained in the structures of thecompounds represented by Chemical Formulae (1) to (7) each independentlyrepresent hydrogen, a methyl group, or a dialkylamino group, and atleast one R₁ be a dialkylamino group.

In addition, it is preferred that, in the above-mentioned dialkylaminogroup, any of the alkyl groups be dialkylamino groups having a carbonnumber of 3 or less. Further, it is more preferred that one of two alkylgroups of the dialkylamino group be a dialkylamino group that is amethyl group. Further, the fact that one alkyl group of the dialkylaminogroup is an alkyl group having a carbon number of 3 or less, and theother alkyl group is a methyl group can further enhance exposuresensitivity. Further, it is particularly preferred that theabove-mentioned dialkylamino group be a dimethylamino group.

Thus, it is preferred that R₁s contained in the structures of thecompounds represented by Chemical Formulae (1) to (7) each independentlyrepresent hydrogen, a methyl group, or a dialkylamino group in which anyof alkyl groups have a carbon number of 3 or less, and at least one R₁be a dialkylamino group.

Further, it is more preferred that R₁s contained in the structures ofthe compounds represented by Chemical Formulae (1) to (7) eachindependently represent hydrogen, a methyl group, or a dialkylaminogroup in which one alkyl group is a methyl group, and at least one R₁ bea dialkylamino group.

Further, it is further more preferred that R₁s contained in thestructures of the compounds represented by Chemical Formulae (1) to (7)each independently represent hydrogen, a methyl group, or a dialkylaminogroup in which one alkyl group is an alkyl group having a carbon numberof 3 or less and the other alkyl group is a methyl group, and at leastone R₁ be a dialkylamino group.

Further, it is particularly preferred that R₁s contained in thestructures of the compounds represented by Chemical Formulae (1) to (7)each independently represent hydrogen, a methyl group, or adimethylamino group, and at least one R₁ be a dimethylamino group.

In the case where the above-mentioned dialkylamino group is contained,R₁s contained in the structures of the compounds represented by ChemicalFormulae (1) to (7) may each independently represent hydrogen, or adialkylamino group in which any of the alkyl groups are dialkylaminogroups having a carbon number of 3 or less, and at least one R₁ may be adialkylamino group.

Further, R₁s contained in the structures of the compounds represented byChemical Formulae (1) to (7) may each independently represent hydrogenor a dialkylamino group in which one alkyl group is a methyl group, andat least one R₁ may be a dialkylamino group.

Further, R₁s contained in the structures of the compounds represented byChemical Formulae (1) to (7) may each independently represent hydrogenor a dialkylamino group in which one alkyl group is an alkyl grouphaving a carbon number of 3 or less and the other alkyl group is amethyl group, and at least one R₁ may be a dialkylamino group.

Further, R₁s contained in the structures of the compounds represented byChemical Formulae (1) to (7) may each independently represent hydrogenor a dimethylamino group, and at least one R₁ may be a dimethylaminogroup.

Further, the case where electron donating groups other than dialylaminogroups and other functional groups are added to the molecular structuresof the compounds represented by Chemical Formulae (1) to (7) isdescribed.

For example, in the case where a hydroxyl group that is an electrondonating group is added, the surface of a formed liquid crystalalignment film is provided with hydrophilicity. It is also a preferredembodiment that a hydroxyl group is not contained, in terms of thephysical properties of the liquid crystal alignment film.

Further, as a halogen group, a phenyl group, a nitro group, and the likeare electron attracting groups, it is preferred that these groups maynot be contained in the molecular structures of the compoundsrepresented by Chemical Formulae (1) to (7). However, they may becontained as long as the effects of the present invention are notimpaired.

Further, the alkylamino group also has an effect useful for enhancingexposure sensitivity as well as the dialkylamino group.

The photo-alignment process for compounds formed using the compoundsrepresented by Chemical Formulae (1) to (7) as materials was conductedby extracting UV rays at 257 nm using a low-pressure mercury lamp as alight source, and irradiating an organic coating film formed on asubstrate with irradiation light linearly polarized with a pilepolarizer in which quartz substrates are laminated on each other atpredetermined irradiation energy.

Further, a liquid crystal display device according to the presentinvention, for example, includes: a pair of substrates at least one ofwhich is transparent; a liquid crystal layer disposed between the pairof substrates; an electrode group formed on at least one substrate ofthe pair of substrates, for applying an electric field to the liquidcrystal layer; a plurality of active elements connected to the electrodegroup; and a liquid crystal alignment film disposed on at least onesubstrate of the pair of substrates, in which the liquid crystalalignment film, which is formed by a photo-alignment process, containspolyimide formed using at least one kind of diamine selected from acompound group B represented by the following Chemical Formulae (8) to(10).

Among R₂s contained in each of the formulae (8) to (10), at least twoR₂s each independently represent a methyl group, an alkoxy group havinga carbon number of 3 or less, a dialkylamino group, or an alkylaminogroup and the other R₂s each independently represent hydrogen or analkyl group having a carbon number of 3 or less.

With the above-mentioned formulae, a liquid crystal display devicehaving a liquid crystal alignment film with satisfactory exposuresensitivity can be obtained. The liquid crystal alignment film providedin the liquid crystal display device obtained in the present inventionhas high sensitivity with respect to the light exposure, while havingcharacteristics such as a high light transmittance (less absorption ofvisible light), heat resistance, high coating film strength, and afunction of aligning liquid crystal molecules (hereinafter, referred toas “alignment capability”).

Diamine represented by Chemical Formulae (8) to (10) react withtetracarboxilic acid dianhydride to form polyamic acid and/or a polyamicacid ester that are precursors of polyimide. Further, the polyamic acidand/or polyamic acid ester form polyimide by an imidization reaction.

A liquid crystal alignment film formed of polyimide and a precursorthereof has characteristics such as a high light transmittance (lessabsorption of visible light), heat resistance, high coating filmstrength, and a function of aligning liquid crystal molecules(hereinafter, referred to as “alignment capability”), and hence, is usedwidely in a liquid crystal display device.

A tetracarboxylic acid dianhydride that reacts with the compoundsrepresented by Chemical Formulae (8) to (10) to form a precursor ofpolyimide is illustrated below.

For example, there are given 1,2,3,4-cyclobutane tetracarboxylic aciddianhydride, 1,2-dimethyl-1,2,3,4-cyclobutane tetracarboxylic aciddianhydride, 1,3-dimethyl-1,2,3,4-cyclobutane tetracarboxylic aciddianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutane tetracarboxylicacid dianhydride, 1,2,3-trimethyl-1,2,3,4-cyclobutane tetracarboxylicacid dianhydride, 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride,and 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride. Thosecompounds may be used alone or in combination of two or more kinds.

Further, the polyamic acid ester can be obtained by, for example,allowing a chlorinated reagent such as thionyl chloride to react withdiesterdicarboxylic acid obtained by allowing alcohol to react with atetracarboxylic acid dianhydride shown above to obtaindiesterdicarboxylic acid chloride, and allowing diamine to react withand to be polycondensed with diesterdicarboxylic acid chloride.

Furthermore, in the case where diamine and a plurality of kinds ofmaterials of the tetracarboxylic acid dianhydrides are mixed, acopolymerized polymer in which a plurality of chemical species arepolymerized with one polymer chain can be obtained.

Polyimide constituting the liquid crystal alignment film is formed byheating polyamic acid and/or a polyamic acid ester that are precursorsof polyimide to allow the imidization reaction to proceed.

Further, it is preferred that polyimide having a high molecular weightconstitute the liquid crystal alignment film in terms of providing theliquid crystal alignment film with alignment capability. The polyamicacid ester is unlikely to cause a decomposition reaction during heating,compared with polyamic acid. More specifically, the polyamic acid esteris unlikely to undergo any decrease in molecular weight in a heatingstep described later. Therefore, it is effective that a polyamic acidester is introduced into a liquid crystal alignment film, in terms ofpreventing the decrease in molecular weight of polyimide.

Next, the step of forming a liquid crystal alignment film containingpolyimide is described. Polyimide is insoluble in a number of oilsolvents. Therefore, in the case of forming a liquid crystal alignmentfilm containing polyimide as a main component, polyamic acid and/or apolyamic acid ester that are precursors of polyimide are dissolved in asolvent to prepare a liquid crystal alignment agent varnish, the varnishis applied to at least one of a pair of substrates, on which the liquidcrystal alignment film is to be formed, followed by heating andimidization, alignment treatment is conducted, and thus, a liquidcrystal alignment film of polyimide is formed.

In addition, in the above-mentioned heating step, the solvent containedin the liquid crystal alignment agent varnish is volatilized, and anorganic coating film of polyamic acid and/or a polyamic acid ester isformed. At the same timing as that in the formation of the organiccoating film, the imidization reaction of polyamic acid and/or apolyamic acid ester proceeds.

It is not always necessary to progress the imidization reaction by 100%,and the imidization reaction is advanced preferably by 40% to 100% ofthe total, more preferably by 50% to 95%, and still more preferably by60% to 90%.

The polyimide and the precursor thereof formed using diamine representedby Chemical Formulae (8) to (10) are preferred for providing alignmentcapability in the photo-alignment process.

When the polyimide and the precursor thereof are irradiated with UVrays, an intermediate is formed in the molecular structures of thepolyimide and the precursor thereof.

The intermediate thus formed is considered to act on photo-alignmenteffectively. In order to perform a photo-alignment process effectively,it is important how easily the intermediate is formed.

The formation of the above-mentioned intermediate in the molecularstructures of the polyimide and the precursor thereof is ascribed to thecleavage of a part of the molecular structures of the polyimide and theprecursor thereof caused by the irradiated UV rays.

Thus, in order to conduct a photo-alignment process effectively, it isnecessary that a part of the molecular structures of polyimide and aprecursor thereof is cleaved at high sensitivity by the irradiated UVrays.

The compounds represented by Chemical Formulae (8) to (10) arecharacterized by having a methyl group that is an electron donatinggroup in the molecular structure thereof, an alkoxy group having acarbon number of 3 or less, a dialkylamino group, or an alkylaminogroup.

The polyamic acid and/or the polyamic acid ester formed using thecompounds represented by Chemical Formulae (8) to (10) have, in themolecular structure thereof, a methyl group, an alkoxy group having acarbon number of 3 or less, a dialkylamino group, or an alkylamino groupeach derived from the molecular structures of the compounds representedby Chemical Formulae (8) to (10).

The inventors of the present invention have found that, in the casewhere polyimide and a precursor thereof formed using the compoundsrepresented by Chemical Formulae (8) to (10) are irradiated with UV raysto be irradiated in a photo-alignment process, an intermediate is formedin molecular structures of the polyimide and the precursor thereof at alow exposure amount.

Thus, the UV irradiation amount in the photo-alignment process can bereduced.

Further, in the case where the compounds represented by ChemicalFormulae (8) to (10) contain an alkoxy group, an alkoxy group having acarbon number of 2 or less is preferred, and a methoxy group is morepreferred.

More specifically, it is more preferred that at least two R₂s among R₂scontained in each of the compounds represented by Chemical Formulae (8)to (10) each independently represent a methyl group, an alkoxy grouphaving a carbon number of 2 or less, a dialkylamino group, or analkylamino group, and the other R₂s each independently representhydrogen or an alkyl group having a carbon number of 3 or less.

Further, it is further preferred that at least two R₂s among R₂scontained in each of the compounds represented by Chemical Formulae (8)to (10) each independently represent a methyl group, a methoxy group, adialkylamino group, or an alkylamino group, and the other R₂s eachindependently represent hydrogen or an alkyl group having a carbonnumber of 3 or less.

In the case where the compounds represented by Chemical Formulae (8) to(10) contain a dialkylamino group, a dialkylamino group having two alkylgroups having a carbon number of 3 or less is preferred, and morepreferably, one of the alkyl groups is a methyl group. Still morepreferably, one alkyl group is a methyl group, and the other alkyl groupis an alkyl group having a carbon number of 3 or less. A dimethylaminogroup is particularly preferred.

In the case where the compounds represented by Chemical Formulae (8) to(10) contain an alkylamino group, it is preferred that the compoundshave an alkyl group having a carbon number of 3 or less. An alkyl grouphaving a carbon number of 2 or less is more preferred. A methylaminogroup is further preferred.

The addition of a methyl group, a dialkylamino group, and an alkylaminogroup to the molecular structures of the compounds represented byChemical Formulae (8) to (10) is effective for enhancing exposuresensitivity, compared with the case where a methoxy group that isanother electron donating group is added.

Accordingly, it is more preferred that at least two R₂s among R₂scontained in each of the compounds represented by Chemical Formulae (8)to (10) each independently represent a methyl group, a dialkylaminogroup, or an alkylamino group, and the other R₂s each independentlyrepresent hydrogen or an alkyl group having a carbon number of 3 orless.

Further, it is further preferred that at least two R₂s among R₂scontained in each of the compounds represented by Chemical Formulae (8)to (10) each independently represent a methyl group, a dimethylaminogroup, or a methylamino group, and the other R₂s each independentlyrepresent hydrogen or an alkyl group having a carbon number of 3 orless.

Further, the dimethylamino group is effective for enhancing exposuresensitivity, compared with a methylamino group, in the case where thedimethylamino group is contained in the compounds represented byChemical Formulae (8) to (10).

Accordingly, it is more preferred that at least two R₂s among R₂scontained in each of the compounds represented by Chemical Formulae (8)to (10) each independently represent a methyl group or a dimethylaminogroup, and the other R₂s each independently represent hydrogen or analkyl group having a carbon number of 3 or less.

Further, of R₂s contained in the compounds represented by ChemicalFormulae (8) to (10), at least two R₂s may represent methyl groups, andthe other R₂s may each independently represent hydrogen or a methylgroup.

Further, of R₂s contained in the compounds represented by ChemicalFormulae (8) to (10), at least two R₂s may represent methyl groups, andthe other R₂s may each independently represent hydrogen.

Further, in the case where a hydroxyl group that is an electron donatinggroup is added, the surface of a formed liquid crystal alignment film isprovided with hydrophilicity. It is also a preferred embodiment that ahydroxyl group is not contained, in terms of the physical properties ofthe liquid crystal alignment film.

Further, as a halogen group, a phenyl group, a nitro group, and the likeare electron attracting groups, it is preferred that these groups maynot be contained in the molecular structures of the compoundsrepresented by Chemical Formulae (8) to (10). However, they may becontained as long as the effects of the present invention are notimpaired.

Further, as the compounds represented by Chemical Formulae (8) to (10)have a naphthalene skeleton, in the case where a photo-alignment processis conducted with respect to the polyimide and the precursor thereofformed using the compounds represented by Chemical Formulae (8) to (10),the photo-alignment process is conducted by extracting UV rays at 300 nmor more using a long arc lamp as a light source, and irradiating anorganic coating film formed on a substrate with irradiation lightlinearly polarized with a pile polarizer in which quartz substrates arelaminated on each other at predetermined irradiation energy.

The naphthalene skeleton has an absorption band in a UV wavelengthregion of 300 nm or more. Therefore, a long arc lamp irradiatingstronger UV rays compared with those of a low-pressure mercury lamp canbe used.

As described above, the exposure amount is calculated by a product of anillumination by an irradiation time.

The time for photo-alignment can be further shortened by using thepolyimide and the precursor thereof formed of the compounds representedby Chemical Formulae (8) to (10) in which enhanced sensitivity isrealized, and by using a lamp having a high illumination such as a longarc lamp.

Further, it is preferred that the diamine represented by ChemicalFormulae (8) to (10) react with at least one kind of tetracarboxylicacid dianhydride selected from the Compound group C represented by thefollowing Chemical Formulae (11) to (17) to form the polyimide.

In the formulae (11) to (17), R₃s each independently represent hydrogen,an alkyl group having a carbon number of 3 or less, or an alkoxy grouphaving a carbon number of 3 or less.

Further, S represents —(CH₂)_(n)—, and n represents an integer of 1 to10.)

The polyimide and the precursor thereof formed when the diaminerepresented by Chemical Formulae (8) to (10) reacts with tetracarboxylicacid dianhydride selected from the Compound group C represented byChemical Formulae (11) to (17) have excellent characteristics in a lighttransmittance, heat resistance, and film strength, as well as exposuresensitivity.

Further, in the formulae (11) to (17), it is more preferred that R₃seach independently represent hydrogen, a methyl group, and an alkoxygroup having a carbon number of 3 or less.

In addition, it is more preferred that at least one of R₃ represent amethyl group or an alkoxy group having a carbon number of 2 or less, interms of enhancing the sensitivity with respect to UV rays in aphoto-alignment process.

Thus, it is more preferred that R₃s each independently representhydrogen, a methyl group, or an alkoxy group having a carbon number of 2or less.

Further, it is more preferred that R₃s each independently representhydrogen, a methyl group, and a methoxy group.

Further, the case where electron donating groups other than thosedescribed above and another functional group are added to the molecularstructures of the compounds represented by Chemical Formulae (11) to(17) is described.

In the case where a hydroxyl group that is an electron donating group isadded, the surface of a formed liquid crystal alignment film is providedwith hydrophilicity. It is also a preferred embodiment that a hydroxylgroup is not contained, in terms of the physical properties of theliquid crystal alignment film.

Further, as a halogen group, a phenyl group, a nitro group, and the likeare electron attracting groups, it is preferred that these groups maynot be contained in the molecular structures of the compoundsrepresented by Chemical Formulae (11) to (17). However, they may becontained as long as the effects of the present invention are notimpaired.

Further, it is preferred that diamine selected from the Compound group Brepresented by Chemical Formulae (8) to (10) be diamine represented bythe following Chemical Formula (18).

In the formula (18), R₄s each independently represent hydrogen, an alkylgroup having a carbon number of 3 or less, an alkoxy group having acarbon number of 3 or less, a dialkylamino group, or an alkylaminogroup, and R₅s each independently represent a methyl group, an alkoxygroup having a carbon number of 3 or less, a dialkylamino group, or analkylamino group.

In the case where an electron donating group is added to R₅, theexposure sensitivity of the polyimide and the precursor thereof formedusing the compound represented by Chemical Formula (18) is moreexcellent.

In the case where R₅ of the compound represented by Chemical Formula(18) contains an alkoxy group, an alkoxy group having a carbon number of2 or less is more preferred, and a methoxy group is further preferred.

Thus, it is preferred that R₅s each independently represent a methylgroup, an alkoxy group having a carbon number of 2 or less, adialkylamino group, or an alkylamino group.

Further, it is further preferred that R₅s each independently represent amethyl group, a methoxy group, a dialkylamino group, or an alkylaminogroup.

In the case where R₅ of the compound represented by Chemical Formula(18) contains a dialkylamino group, it is preferred that thedialkylamino group have two alkyl groups having a carbon number of 3 orless, and more preferably, one alkyl group represents a methyl group. Adimethylamino group is further preferred.

In the case where R₅ of the compound represented by Chemical Formula(18) contains an alkylamino group, it is preferred that the alkylaminogroup have an alkyl group having a carbon number of 3 or less, and analkyl group having a carbon number of 2 or less is more preferred. Amethylamino group is further preferred.

Further, it is preferred that R₅ of the compound represented by ChemicalFormula (18) contain a methyl group, a dialkylamino group, or analkylamino group, compared with the case where R₅ contains a methoxygroup.

Thus, it is more preferred that R₅s each independently represent amethyl group, a dialkylamino group, or an alkylamino group.

Further, R₅s may each independently represent a methyl group or analkylamino group.

Further, R₅s may each independently represent a methyl group or adialkylamino group.

Further, both of the two R₅s may each independently represent a methylgroup in the compound represented by Chemical Formula (18).

In the case where R₄ of the compound represented by Chemical Formula(18) contains an alkoxy group, an alkoxy group having a carbon number of2 or less is more preferred, and a methoxy group is further preferred.

Thus, it is more preferred that R₄s each independently representhydrogen, an alkyl group having a carbon number of 3 or less, an alkoxygroup having a carbon number of 2 or less, a dialkylamino group, or analkylamino group.

Thus, it is further preferred that R₄s each independently representhydrogen, an alkyl group having a carbon number of 3 or less, a methoxygroup, a dialkylamino group, or an alkylamino group.

In the case where R₄ of the compound represented by Chemical Formula(18) contains an alkyl group, an alkyl group having a carbon number of 2or less is more preferred, and a methyl group is further preferred.

Thus, it is more preferred that R₄s each independently representhydrogen, an alkyl group having a carbon number of 2 or less, a methoxygroup, a dialkylamino group, or an alkylamino group.

Further, it is further preferred that R₄s each independently representhydrogen, a methyl group, a methoxy group, a dialkylamino group, or analkylamino group.

In the case where R₄ of the compound represented by Chemical Formula(18) contains a dialkylamino group, it is preferred that thedialkylamino group have two alkyl groups having a carbon number of 3 orless, and more preferably, one alkyl group represents a methyl group. Adimethylamino group is further preferred.

In the case where R₄ of the compound represented by Chemical Formula(18) contains an alkylamino group, it is preferred that the alkylaminogroup have an alkyl group having a carbon number of 3 or less, and analkyl group having a carbon number of 2 or less is more preferred. Amethylamino group is further preferred.

Thus, it is more preferred that R₄s each independently representhydrogen, a methyl group, a methoxy group, a dimethylamino group, or anmethylamino group.

Further, R₄s may each independently represent hydrogen or a methylgroup.

Further, R₄s may each independently represent hydrogen or a methoxygroup.

Further, R₄s may each independently represent hydrogen or adimethylamino group.

Further, R₄s may each independently represent hydrogen or an alkylaminogroup.

Further, R₄s may each independently represent hydrogen, a dimethylaminogroup, or an alkylamino group.

In addition, both of the two R₄ may be hydrogen in the compoundrepresented by Chemical Formula (18). Further, both of the two R₄ mayrepresent methyl groups.

R₄ and R₅ of the compound represented by Chemical Formula (18) describedabove may be appropriately combined.

For example, R₄s may each independently represent hydrogen or a methylgroup, and R₅s may each independently represent a methyl group, adialkylamino group, or an alkylamino group.

Further, R₄s may each independently represent hydrogen or a methylgroup, and R₅s may each independently represent a methyl group or analkylamino group.

Further, R₄s may each independently represent hydrogen or a methoxygroup, and R₅s may each independently represent a methyl group, adialkylamino group, or an alkylamino group.

Further, R₄s may each independently represent hydrogen or adimethylamino group, and R₅s may each independently a methyl group, adialkylamino group, or an alkylamino group.

Further, R₄s may each independently represent hydrogen or an alkylaminogroup, and R₅s may each independently represent a methyl group, adialkylamino group, or an alkylamino group.

Further, R₄s may each independently represent hydrogen, a dimethylaminogroup, or an alkylamino group, and R₅s may each independently representa methyl group, a dialkylamino group, or an alkylamino group.

Further, R₄s may each independently represent hydrogen or a methylgroup, and R₅s may each independently represent a methyl group or analkylamino group.

Further, R₄s may each independently represent hydrogen or a methoxygroup, and R₅s may each independently represent a methyl group or analkylamino group.

Further, R₄s may each independently represent hydrogen or adimethylamino group, and R₅s may each independently represent a methylgroup or an alkylamino group.

Further, R₄s may each independently represent hydrogen or an alkylaminogroup, and R₅s may each independently represent a methyl group or analkylamino group.

Further, R₄s may each independently represent hydrogen, a dimethylaminogroup, or an alkylamino group, and R₅s may each independently representa methyl group or an alkylamino group.

Further, R₄s may each independently represent hydrogen or a methylgroup, and R₅s may each independently represent a methyl group or adialkylamino group.

Further, R₄s may each independently represent hydrogen or a methoxygroup, and R₅s may each independently represent a methyl group or adialkylamino group.

Further, R₄s may each independently represent hydrogen or adimethylamino group, and R₅s may each independently represent a methylgroup or a dialkylamino group.

Further, R₄s may each independently represent hydrogen or an alkylaminogroup, and R₅s may each independently represent a methyl group or adialkylamino group.

Further, R₄s may each independently represent hydrogen, a dimethylaminogroup, or an alkylamino group, and R₅s may each independently representa methyl group or a dialkylamino group.

Further, the case where an electron donating group other than thosedescribed above and another functional group are added to the molecularstructure of the compound represented by Chemical Formula (18) isdescribed.

For example, in the case where a hydroxyl group that is an electrondonating group is added, the surface of a formed liquid crystalalignment film is provided with hydrophilicity. It is also a preferredembodiment that a hydroxyl group is not contained, in terms of thephysical properties of the liquid crystal alignment film.

Further, as a halogen group, a phenyl group, a nitro group, and the likeare electron attracting groups, it is preferred that these groups be notcontained in the molecular structure of the compound represented byChemical Formula (18). However, they may be contained as long as theeffects of the present invention are not impaired.

It is more preferred that the diamine represented by Chemical Formula(18) react with at least one kind of tetracarboxylic acid dianhydrideselected from the Compound group C represented by the following ChemicalFormulae (11) to (17) to form polyimide and a precursor thereof.

In the formulae (11) to (17), R₃s each independently represent hydrogen,an alkyl group having a carbon number of 3 or less, or an alkoxy grouphaving a carbon number of 3 or less.

Further, S represents —(CH₂)_(n)—, and n represents an integer of 1 to10.

The polyimide and the precursor thereof formed when the diaminerepresented by Chemical Formula (18) reacts with tetracarboxylic aciddianhydride selected from the Compound group C represented by ChemicalFormulae (11) to (17) have excellent characteristics in a lighttransmittance, heat resistance, and film strength, as well as exposuresensitivity.

Further, it is more preferred that R₃s each independently representhydrogen, a methyl group, or an alkoxy group having a carbon number of 3or less.

In addition, it is more preferred that at least one of R₃s represent amethyl group or an alkoxy group having a carbon number of 2 or less, interms of enhancing the sensitivity with respect to UV rays in aphoto-alignment process.

Thus, it is more preferred that R₃s each independently representhydrogen, a methyl group, or an alkoxy group having a carbon number of 2or less.

Further, it is more preferred that R₃s each independently representhydrogen, a methyl group, and a methoxy group.

Further, the case where electron donating groups other than thosedescribed above and other functional groups are added to the molecularstructures of the compounds represented by Chemical Formulae (11) to(17) is described.

In the case where a hydroxyl group that is an electron donating group isadded, the surface of a formed liquid crystal alignment film is providedwith hydrophilicity. It is also a preferred embodiment that a hydroxylgroup is not contained, in terms of the physical properties of theliquid crystal alignment film.

Further, as a halogen group, a phenyl group, a nitro group, and the likeare electron attracting groups, it is preferred that these groups arenot contained in the molecular structures of the compounds representedby Chemical Formulae (11) to (17). However, they may be contained aslong as the effects of the present invention are not impaired.

Example 1

A liquid crystal display device according to an embodiment of thepresent invention is described with reference to FIG. 1 and FIGS. 2A,2B, and 2C.

FIG. 1 is a schematic cross-sectional view illustrating the vicinity ofone pixel in the liquid crystal display device according to thisexample. FIG. 2 are schematic views of an active matrix substrateillustrating a configuration of the vicinity of one pixel of the liquidcrystal display device according to this example, in which FIG. 2A is aplan view, FIG. 2B is a cross-sectional view taken along the line 2B-2Billustrated in FIG. 2A, and FIG. 2C is a cross-sectional view takenalong the line 2C-2C illustrated in FIG. 2A. Further, FIG. 1 correspondsto a part of a cross section taken along the line 2B-2B illustrated inFIG. 2A.

FIGS. 2B and 2C schematically emphasize configurations of main portions,and do not correspond one by one to cut portions of the line 2B-2B andthe line 2C-2C in FIG. 2A. For example, a semiconductor film 116 is notshown in FIG. 2B, and only one through-hole 118 that connects a commonelectrode 103 and a common electrode line (common line) 120 isrepresentatively illustrated in FIG. 2C.

In this embodiment, scanning lines (gate lines) 104 and the commonelectrode line 120 which are made of chrome (Cr) are arranged on a glasssubstrate 101 as the active matrix substrate, and a gate insulating film107 made of silicon nitride is so formed as to cover the scanning lines104 and the common electrode line 120.

Further, the semiconductor film 116 made of amorphous silicon orpolysilicon is arranged above each of the scanning lines 104 through thegate insulating film 107, and functions as an active layer of each thinfilm transistor (TFT) 115 serving as the active element.

Further, each signal line (drain electrode) 106 made ofchrome/molybdenum (Cr.Mo) and each pixel electrode (source electrode)105 made of an indium tin oxide (ITO) film are so arranged as to besuperimposed on a part of the pattern of the semiconductor film 116, anda protective insulating film 108 made of silicon nitride is so formed asto cover all of those components.

Further, as illustrated in FIG. 2C, the common electrodes 103 thatconnect to the common electrode line 120 through the through-hole 118formed through the gate insulating film 107 and the protectiveinsulating film 108 are arranged on an organic protective film (overcoatlayer) 112.

Further, as illustrated in FIG. 2A, the common electrodes 103 drawn fromthe common electrode line 120 through the through-hole 118 are so formedas to face the pixel electrodes 105 in a region of one pixel in a planarfashion.

In this embodiment, the pixel electrodes 105 are arranged below theprotective insulating film 108 which is disposed below the organicprotective film 112, and the common electrodes 103 are arranged on theorganic protective film 112.

One pixel is configured in a region sandwiched between the plurality ofpixel electrodes 105 and the plurality of common electrodes 103.

Further, a liquid crystal alignment film 109 is formed on a surface ofthe active matrix substrate on which the unit pixels configured asdescribed above are arranged in matrix, that is, on the organicprotective film 112 on which the common electrodes 103 are formed.

On the other hand, as illustrated in FIG. 1, a color filter layer 111 isarranged on the glass substrate 102 constituting the counter substrateso as to be partitioned by a light shield film (black matrix) 113 foreach pixel. Further, the color filter layer 111 and the light shieldfilm 113 are covered with the organic protective film 112 made of atransparent insulating material. Further, the liquid crystal alignmentfilm 109 is also formed on the organic protective film 112 to configurea color filter substrate.

Those liquid crystal alignment films 109 are provided with liquidcrystal alignment capability by irradiation of linearly polarizedultraviolet rays which are extracted with the use of a pile polarizer inwhich quartz plates are laminated on each other with a low-pressuremercury lamp as a light source.

The glass substrate 101 constituting the active matrix substrate and theglass substrate 102 constituting the color filter substrate are arrangedto face each other at the surfaces of the liquid crystal alignment films109, and a liquid crystal composition layer (liquid crystal layer) 110 bmade up of liquid crystal molecules 110 a are arranged between the glasssubstrate 101 and the glass substrate 102.

Further, on the respective outer surfaces of the glass substrate 101constituting the active matrix substrate and the glass substrate 102constituting the color filter substrate, polarization plates 114 areformed.

In the above-mentioned manner, the active matrix liquid crystal displaydevice (TFT liquid crystal display device) using the TFT 115 isconfigured. In the TFT liquid crystal display device, the liquid crystalmolecules 110 a constituting the liquid crystal composition layer 110 bare aligned substantially in parallel to the surfaces of the glasssubstrates 101 and 102 which face each other at the time of applying noelectric field. The liquid crystal molecules 110 a are homogeneouslyaligned in a state in which the liquid crystal molecules 110 a aredirected in an initial alignment direction regulated by thephoto-alignment process.

Here, when a voltage is applied to the scanning lines 104 to turn on theTFT 115, an electric field 117 is applied to the liquid crystalcomposition layer 110 b due to a potential difference between the pixelelectrode 105 and the common electrodes 103. The liquid crystalmolecules 110 a constituting the liquid crystal composition layer 110 bare turned to the electric field direction due to an interaction betweena dielectric anisotropy of the liquid crystal composition layer 110 band the electric field. In this situation, the refractive anisotropy ofthe liquid crystal composition layer 110 b and the action of thepolarization plates 114 can change the light transmittance of the liquidcrystal display device for display.

Further, the organic protective film 112 may be made of a thermosettingresin such as an acrylic resin, an epoxy acrylic resin or a polyimideresin which are excellent in the insulating property and thetransparency. Further, the organic protective film 112 may be made of alight curing transparent resin, or an inorganic material such as apolysiloxane resin. Further, the organic protective film 112 may alsofunction as the liquid crystal alignment film 109.

As described above, according to this example, the liquid crystalalignment capability of the liquid crystal alignment film 109 isperformed by using not a rubbing alignment process that directly rubsthe liquid crystal alignment film 109 with a buff cloth, but anon-contact photo-alignment method. As a result, uniform alignment canbe given to the entire surface of the display region without localdisturbance of alignment in the vicinity of the electrodes.

In general, in the in-plane switching (IPS) system, no interface tiltwith the substrate surface is required in principle unlike the verticalelectric field system represented by the conventional twisted nematic(TN) system. It is known that the viewing angle characteristic is moreimproved as the interface tilt angle becomes smaller. A smallerinterface tilt angle is desired even in the photo-aligned liquid crystalalignment film. In particular, when the interface tilt angle is set to 1degree or less, changes in color and brightness due to the viewing angleof the liquid crystal display device can be remarkably suppressed, whichis effective.

Subsequently, as a method of manufacturing the liquid crystal displaydevice of this example, formation of the liquid crystal alignment filmby using a rubbingless alignment method for a liquid crystal alignmentfilm is described in detail. A flow of a process of forming the liquidcrystal alignment film according to this example includes the followingsteps (1) to (4).

Step (1): Coating and formation of varnish containing componentsconstituting the liquid crystal alignment film (a uniform coating filmis formed on the entire surface of the display region).

Step (2): Imidization baking of the organic coating film (removal ofvarnish solvent and polyimidization high in heat resistance areenhanced).

Step (3): Impartation of the liquid crystal alignment capability byirradiation of the polarized light (the uniform alignment capability isimparted to the display region).

Step (4): Enhancement and stabilization of the alignment capability (byheating, infrared radiation, far infrared radiation, electron beamirradiation or radiation exposure).

The liquid crystal alignment film is formed through the above-mentionedfour-step process. However, the present invention is not limited to theorder of the process of the above-mentioned steps (1) to (4). Moreover,further effects are expected in the case of the following cases (a) and(b).

(a) The above-mentioned steps (3) and (4) are so processed as totemporally overlap with each other to accelerate the liquid crystalalignment capability impartation and induce a cross-linking reaction orthe like. As a result, the liquid crystal alignment film can be furthereffectively formed.

(b) In the case of using the heating, the infrared radiation, or the farinfrared radiation of the above-mentioned step (4), the above-mentionedsteps (2), (3) and (4) are allowed to temporally overlap with eachother. As a result, the process of the above-mentioned step (4) can alsofunction as the imidization process of the above-mentioned step (2), andhence the liquid crystal alignment film can be formed in a short time.

Subsequently, a specific manufacturing method of this example isdescribed. A glass substrate having a thickness of 0.7 mm whose surfacehas been polished is used as the glass substrate 101 constituting theactive matrix substrate and the glass substrate 102 constituting thecolor filter substrate.

The TFT 115 formed on the glass substrate 101 includes the pixelelectrode 105, the signal line 106, the scanning line 104, and thesemiconductor film (amorphous silicon) 116.

All of the scanning line 104, the common electrode line 120, and thesignal line 106 were formed by patterning a chrome film, and an intervalbetween the pixel electrode 105 and each of the common electrodes 103was set to 7 μm. In this embodiment, the common electrodes 103 and thepixel electrode 105 were formed of the ITO film so as to constitutetransparent electrodes to achieve higher brightness characteristics.Alternatively, the common electrodes 103 and the pixel electrode 105 mayalso be formed of a chrome film which is low in resistance and easy inpatterning, instead of the ITO film.

The gate insulating film 107 and the protective insulating film 108 weremade of silicon nitride, and the thicknesses were each set to 0.3 μm. Anacrylic resin was coated on those films, and a heat treatment at 220° C.for 1 hour was conducted to form the transparent and insulating organicprotective film 112.

Then, the through-hole 118 was formed up to the common electrode line120 through photolithography and etching process as illustrated in FIG.2C, and the common electrodes 103 that connect to the common electrodeline 120 were formed by patterning.

As a result, as illustrated in FIG. 2A, the pixel electrode 105 wasarranged among the three common electrodes 103 within the unit pixel(one pixel) to form the active matrix substrate which has 1024×3×768pixels, which includes 1024×3 (corresponding to R, G, and B) signallines 106 and 768 scanning lines 104.

In Example 1, the following film was used as the liquid crystalalignment film 109.

First, a tetracarboxylic acid dianhydride represented by the followingChemical formula (201) and p-phenylenediamine were polycondensed in amolar ratio of 1:1 to obtain a polyamic acid.

After that, 5 parts by weight of the polyamic acid and 95 parts byweight of a solvent capable of dissolving the polyamic acid were mixedto prepare liquid crystal alignment agent varnish.

The solvent can be selected appropriately from, for example,dimethylacetamide, γ-butyrolactone, and butyl cellosolve for use.

The liquid crystal alignment agent varnish was applied to a substrate byspin-coating and heated at 230° C. for 10 minutes to form an organiccoating film. After that, the organic coating film was irradiated withpolarized UV rays having a wavelength of 257 nm, adjusting theillumination and the irradiation time so as to obtain an exposure amountof 2.0 J/cm², thereby performing a photo-alignment process. Thus, theliquid crystal display device of Example 1 was obtained.

Reference Example 1

In Reference Example 1, the following was used as the liquid crystalalignment film 109. A liquid crystal display device was manufactured bythe same method as that of Example 1, except for the composition of theliquid crystal alignment film 109.

First, a tetracarboxylic acid dianhydride represented by the followingChemical formula (202) and p-phenylenediamine were polycondensed in amolar ratio of 1:1 to obtain a polyamic acid.

Next, 5 parts by weight of the polyamic acid and 95 parts by weight of asolvent capable of dissolving the polyamic acid were mixed to prepareliquid crystal alignment agent varnish.

The solvent can be selected appropriately from, for example,dimethylacetamide, γ-butyrolactone, and butyl cellosolve for use.

In the same manner as in Example 1, the liquid crystal alignment agentvarnish was applied to a substrate by spin-coating and heated at 230° C.for 10 minutes to form an organic coating film. After that, a rubbingalignment process was performed. Thus, the liquid crystal display deviceof Reference Example 1 was obtained.

Comparative Example 1

In Comparative Example 1, the following was used as the liquid crystalalignment film 109. A liquid crystal display device was manufactured bythe same method as that of Example 1, except for the composition of theliquid crystal alignment film 109.

First, a tetracarboxylic acid dianhydride represented by the followingChemical formula (202) and p-phenylenediamine were polycondensed in amolar ratio of 1:1 to synthesize a polyamic acid.

After that, 5 parts by weight of the polyamic acid and 95 parts byweight of a solvent capable of dissolving the polyamic acid were mixedto prepare liquid crystal alignment agent varnish.

The solvent can be selected appropriately from, for example,dimethylacetamide, γ-butyrolactone, and butyl cellosolve for use.

The liquid crystal alignment agent varnish was applied to a substrate byspin-coating and heated at 230° C. for 10 minutes to form an organiccoating film. After that, the organic coating film was irradiated withpolarized UV rays having a wavelength of 257 nm, adjusting theillumination and the irradiation time so as to obtain an exposure amountof 2.0 J/cm², thereby performing a photo-alignment process. Thus, theliquid crystal display device of Comparative Example 1 was obtained.

A voltage was applied to the liquid crystal display devices manufacturedin Example 1, Reference Example 1, and Comparative Example 1, and therelationship between the light transmittance strength and the voltagewas measured. Thus, the sensitivity of the liquid crystal alignmentfilms provided in the liquid crystal display devices were studied.

As a result of the measurement and the comparison between Example 1 andReference Example 1, the relationships between the light transmittancestrength and the voltage were equivalent. Thus, it is understood that,in the liquid crystal display device manufactured in Example 1, analignment process equivalent to that of Reference Example 1 subjected tothe rubbing alignment process was conducted.

In order for the liquid crystal display device of Comparative Example 1to obtain performance equivalent to that of the liquid crystal displaydevice of Example 1, it was necessary to adjust the irradiation time ofthe polarized UV ray having a wavelength of 257 nm to be applied to theorganic coating film so that the exposure amount was 10.0 J/cm².

That is, it was found that the photo-alignment process can be conductedat an exposure amount of about ⅕, by adding a dimethylamino group to thetetracarboxylic acid dianhydride.

The exposure amount is obtained by a product of the illumination by theirradiation time. Therefore, in the case where a photo-alignment processwas conducted from a light source with the identical illumination, theirradiation time was shortened to about ⅕ by allowing thetetracarboxylic acid dianhydride to have a structure of a dimethylaminogroup in the organic coating film.

Example 2

In Example 2, the following was used as the liquid crystal alignmentfilm 109. A liquid crystal display device was manufactured by the samemethod as that of Example 1, except for the composition of the liquidcrystal alignment film 109.

First, a diamine represented by the following Chemical Formula (204) anda tetracarboxylic acid dianhydride represented by the following Chemicalformula (205) were polycondensed in a molar ratio of 1:1 to obtain apolyamic acid.

Next, 5 parts by weight of the polyamic acid and 95 parts by weight of asolvent capable of dissolving the polyamic acid were mixed to prepareliquid crystal alignment agent varnish.

The solvent can be selected appropriately from, for example,dimethylacetamide, γ-butyrolactone, and butyl cellosolve for use.

The liquid crystal alignment agent varnish was applied to a substrate byspin-coating and heated at 230° C. for 10 minutes to form an organiccoating film. After that, the organic coating film was irradiated withpolarized UV rays using a long arc lamp, adjusting the illumination andthe irradiation time so as to obtain an exposure amount of 1.0 J/cm²,thereby performing a photo-alignment process. Thus, the liquid crystaldisplay device of Example 2 was obtained.

Reference Example 2

In Reference Example 2, the following was used as the liquid crystalalignment film 109. A liquid crystal display device was manufactured bythe same method as that of Example 1, except for the composition of theliquid crystal alignment film 109.

First, a diamine represented by the following Chemical formula (204) anda tetracarboxylic acid dianhydride represented by the following Chemicalformula (205) were polycondensed in a molar ratio of 1:1 to synthesize apolyamic acid.

Next, 5 parts by weight of the polyamic acid and 95 parts by weight of asolvent capable of dissolving the polyamic acid were mixed to prepareliquid crystal alignment agent varnish.

The solvent can be selected appropriately from, for example,dimethylacetamide, γ-butyrolactone, and butyl cellosolve for use.

The liquid crystal alignment agent varnish was applied to a substrate byspin-coating and heated at 230° C. for 10 minutes to form an organiccoating film. After that, a rubbing process was performed. Thus, theliquid crystal display device of Reference Example 2 was obtained.

Comparative Example 2

In Comparative Example 2, the following was used as the liquid crystalalignment film 109. A liquid crystal display device was manufactured bythe same method as that of Example 1, except for the composition of theliquid crystal alignment film 109.

First, p-phenylenediamine and a tetracarboxylic acid dianhydriderepresented by the following Chemical formula (205) were polycondensedin a molar ratio of 1:1 to obtain a polyamic acid.

Next, 5 parts by weight of the polyamic acid and 95 parts by weight of asolvent capable of dissolving the polyamic acid were mixed to prepareliquid crystal alignment agent varnish.

The solvent can be selected appropriately from, for example,dimethylacetamide, γ-butyrolactone, and butyl cellosolve for use.

The liquid crystal alignment agent varnish was applied to a substrate byspin-coating and heated at 230° C. for 10 minutes to form an organiccoating film. After that, the organic coating film was irradiated withpolarized UV rays having a wavelength of 257 nm, adjusting theirradiation time so as to obtain performance equivalent to that ofExample 2, thereby performing a photo-alignment process. Thus, theliquid crystal display device of Comparative Example 2 was obtained.

A voltage was applied to the liquid crystal display devices manufacturedin Example 2 and Comparative Example 2, and the relationship between thelight transmittance strength and the voltage was measured. Thus, thesensitivity of the liquid crystal alignment films provided in the liquidcrystal display devices were studied.

As a result of the measurement and the comparison between Example 2 andReference Example 2, the relationships between the light transmittancestrength and the voltage were equivalent. Thus, it is understood that,in the liquid crystal display device manufactured in Example 2, analignment process equivalent to that of Reference Example 2 subjected tothe rubbing alignment process was conducted.

In Comparative Example 2, in order to obtain the results equivalent tothose of Example 2, it was necessary to irradiate the organic coatingfilm with the UV ray having a wavelength of 257 nm for a time that isabout three times the irradiation time of Example 2.

Accordingly, it was found that a photo-alignment process can beconducted for an irradiation time that is about ⅓ of the conventionalexample, by having a naphthalene skeleton and further adding methylgroups to 2,6-positions.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaim cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A liquid crystal display device, comprising: apair of substrates at least one of which is transparent; a liquidcrystal layer disposed between the pair of substrates; an electrodegroup formed to one substrate of the pair of substrates, for applying anelectric field to the liquid crystal layer, the electric field having acomponent parallel to the one substrate; a plurality of active elementsconnected to the electrode group; and a liquid crystal alignment filmdisposed to at least one substrate of the pair of substrates, whereinthe liquid crystal alignment film, which is formed by a photo-alignmentprocess, contains polyimide formed using at least one kind oftetracarboxylic acid dianhydride selected from a compound group Arepresented by the following Chemical Formulae (1) to (5):

where R₁s each independently represent hydrogen, an alkyl group having acarbon number of 3 or less, or a dialkylamino group, and at least one R₁represents a dialkylamino group, where S represents —(CH₂) n-, and nrepresents an integer of 1 to
 10. 2. The liquid crystal display deviceaccording to claim 1, wherein any alkyl group of the dialkylamino grouprepresents a dialkylamino group having a carbon number of 3 or less. 3.The liquid crystal display device according to claim 1, wherein thedialkylamino group is a dimethylamino group.
 4. The liquid crystaldisplay device according to claim 1, wherein an interface tilt anglebetween the liquid crystal layer and the liquid crystal alignment filmis set to 1 degree or less.
 5. The liquid crystal display deviceaccording to claim 1, wherein the tetracarboxylic acid dianhydridereacts with at least one kind of diamine selected from a compound groupB represented by the following Chemical Formulae (8) to (10):

where among R₂ s contained in each of the formulae (8) to (10), at leasttwo R₂ s each independently represent a methyl group, an alkoxy grouphaving a carbon number of 3 or less, a dialkylamino group, or analkylamino group and the other R₂ s each independently representhydrogen or an alkyl group having a carbon number of 3 or less.
 6. Theliquid crystal display device according to claim 5, wherein the diamineis represented by the following Chemical Formula (18):

where R₄ s each independently represent hydrogen, an alkyl group havinga carbon number of 3 or less, an alkoxy group having a carbon number of3 or less, a dialkylamino group, or an alkylamino group; and R₅ s eachindependently represent a methyl group, an alkoxy group having a carbonnumber of 3 or less, a dialkylamino group, or an alkylamino group. 7.The liquid crystal display device according to claim 1, wherein thepolyimide is formed by imidizing a polyimide precursor formed using theat least one kind of tetracarboxylic acid dianhydride selected from thecompound group A, wherein 50% to 95% of a total amount of the polyimideprecursor is imidized to form the polyimide.
 8. A liquid crystalalignment film varnish comprising a polyamic acid and/or a polyamic acidester formed using at least one kind of tetracarboxylic acid dianhydrideselected from a compound group A represented by the following ChemicalFormulae (1) to (5), wherein the liquid crystal alignment film varnishis for a photo-alignment process

where R₁s each independently represent hydrogen, an alkyl group having acarbon number of 3 or less, or a dialkylamino group, and at least one R₁represents a dialkylamino group, where S represents —(CH₂)n-, and nrepresents an integer of 1 to
 10. 9. The liquid crystal alignment filmvarnish according to claim 8, wherein any alkyl group of thedialkylamino group represents a dialkylamino group having a carbonnumber of 3 or less.
 10. The liquid crystal alignment film varnishaccording to claim 8, wherein the dialkylamino group is a dimethylaminogroup.
 11. The liquid crystal alignment film varnish according to claim8, wherein the tetracarboxylic acid dianhydride reacts with at least onekind of diamine selected from a compound group B represented by thefollowing Chemical Formulae (8) to (10):

where among R₂s contained in each of the formulae (8) to (10), at leasttwo R₂s each independently represent a methyl group, an alkoxy grouphaving a carbon number of 3 or less, a dialkylamino group, or analkylamino group and the other R₂ s each independently representhydrogen or an alkyl group having a carbon number of 3 or less.
 12. Theliquid crystal alignment film varnish according to claim 11, wherein thediamine is represented by the following Chemical Formula (18):

where R₄ s each independently represent hydrogen, an alkyl group havinga carbon number of 3 or less, an alkoxy group having a carbon number of3 or less, a dialkylamino group, or an alkylamino group; and R₅ s eachindependently represent a methyl group, an alkoxy group having a carbonnumber of 3 or less, a dialkylamino group, or an alkylamino group.